Reversible Reduction and Reoxidation of Entire Thin Films of Octacyanophthalocyanine

Abstract

The electrochemical properties of solid films of 3,9,10,16,17,23, Zn(II), Cu(II)] were studied by cyclic voltammetry in aqueous electrolytes. The thin (10-100 rim) film electrodes show remarkably stable electrochromic redox behavior, and the charge exchanged in the cathodic and anodic waves, respectively, was found to be between 2 and 3 F/tool for scan rates up to 400 mV/s. For charge compensation, the intercalation of cations is required. At low pH values (intercalation of protons), nernstian behavior was observed, while in alkaline solutions the intercalation of the cations LP, Na t, or K ~ into the solid film was found to be the rate-determining step. From the halfwidth of the current waves, the number of electrons involved in the overall reaction was inferred and found to be different in acid and alkaline solutions. Compared to unsubstituted phthalocyanines 1, the characteristic qualities of the electrodes are associated with the high electric conductivity of 2 and the electron accepting properties of the substituents of the ligand.

Electrochromic Switching of Evaporated Thin Films of Bulky, Electronic Deficient Metallo-Phthalocyanines

“…the ∼3.5 Â 10 À12 cm 2 s À1 literature values for K þ in F 16 PcCu. The surprisingly similar values for Li þ /K þ , tightly/loosely packed films, perhaps underscore the importance of specific interactions between the charge-balancing counterions and the reduced Pc À• rings rather than purely electrostatic interactions.…”

“…Film reconstructions were observed earlier for thin phthalocyanine films upon their reduction and reoxidation. 16,18À20 However, this conditioning phase was observed to a greater extent for F 64 Pc despite rather little molecular coupling in the solid state, and in particular for F 64 PcVO 31 caused by clear establishment of conductive ionic pathways within the well-defined solid-state structure of F 64 PcVO.…”

“…7,8 Since p-type characteristics are observed for a number of organic semiconductors including unsubstituted phthalocyanines (Pc), substitution by electronwithdrawing substituents is of special interest. The use of metal complexes of perfluorinated phthalocyanine F 16 Pc has been well established over the last years as one of the most promising ways to induce stable n-type conduction in organic semiconductor thin films. 2 Aside from their application as semiconductors, phthalocyanine films might also be of interest as electrochromic layers because of their strong light absorption, i.e., high molar extinction coefficients, 9 and the strong changes of color upon oxidation or reduction.…”

“…12,13 Unlike unsubstituted phthalocyanines that, upon irreversible oxidation, suffer corrosion as thin films, 14 films of double decker lanthanide phthalocyanines 15 or substituted phthalocyanines with electron-withdrawing substituents exhibit largely reversible electrochromic reductions. 12,16À21 With the exception of tetrapyridotetraazaporphyrins 17,21 or tetrapyrazinotetraaazaporphyrins, 18,19 which contain N-heteroatoms in the benzogroups, F 16 Pc appear to be the most versatile and reliable phthalocyanine molecules for film preparation and reversible electrochromic switching. 20 For technical electrochromism, 50À100 nm films are needed, thicker than a monolayer but clearly below the thickness of traditional inorganic films, e.g., those formed by tungsten oxide.…”

Spectral investigation of interaction of copper phthalocyanine with nitrogen dioxide

“…The redox behaviour was investigated both for monophthalocyanine solutions [22,23] and for their films [22,24,25].…”